linux-kernel - Re: [RFC 7/12][PATCH] SCHED_DEADLINE: signal delivery when overrunning

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Message-ID: <1263375023.3853.3.camel@Palantir>
Date:	Wed, 13 Jan 2010 10:30:23 +0100
From:	Raistlin <raistlin@...ux.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	michael trimarchi <michael@...dence.eu.com>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	Chris Friesen <cfriesen@...tel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Henrik Austad <henrik@...tad.us>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Sven-Thorsten Dietrich <sven@...bigcorporation.com>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
	"giuseppe.lipari" <giuseppe.lipari@...up.it>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [RFC 7/12][PATCH] SCHED_DEADLINE: signal delivery when
 overrunning

On Mon, 2009-12-28 at 15:19 +0100, Peter Zijlstra wrote: 
> > A runtime overrun will be quite common, e.g. due to coarse execution time
> > accounting, wrong parameter assignement, etc.
> > A deadline miss --since the deadlines the scheduler sees are ``scheduling
> > deadlines'' which have not necessarily to be equal to task's deadlines-- is
> > much more unlikely, and should only happen in an overloaded system.
> 
> Right, I think its much better to not do this in posix-cpu-timers.c,
> that code is shite.
> 
> Its probably possible to set SIGXCPU pending and raise TIF_SIGPENDING
> from within the scheduler code, and that will be triggered when we
> return to userspace.
> 
Ok, this sounds a lot better to me too... I'll go for this!

> That also gets rid of that coarse execution time accounting muck, since
> the scheduler has ns accurate accounting.
> 
Yes --at least when the hrtick is enabled-- I agree that this is another
very interesting benefit of this approach.

It'll be done like this in the next version of the patchset I'm
preparing.

Thanks for the answer and regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa  (Italy)

http://blog.linux.it/raistlin / raistlin@...ga.net /
dario.faggioli@...ber.org

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